Microstructural characteristics of spinel powders

Mg-Al spinel powders have been prepared by thermal decomposition of a mixture of: A - aluminium and magnesium nitrates; B - aluminium and magnesium hydroxides; and C - aluminium hydroxide and magnesium oxalate. The initial and the final powders were both characterized by specific surface area measurements, mercury intrusion porosimetry, X-ray diffraction, and scanning electron microscopy. The results showed that the preparation process sharply influences the final microstructure of the spinel powders. In particular while the shape and particle dimensions of the samples prepared by mixture of aluminium and magnesium nitrates are mainly influenced by crushing process, the preparation via mixed magnesium and aluminium hydroxides precipitation permits use of spinel formation temperatures as low as 350°C. Characteristically this powder is very uniform and consists of small particle sizes (0.1 micrometers).